Field of the Invention
The present invention relates to a zoom lens advantageously applicable to an image pickup optical system for use in an image pickup apparatus, such as a digital still camera, a video camera, a monitoring camera, a broadcasting camera, or a silver-halide film camera.
Description of the Related Art
Recent image pickup apparatuses are highly functional and compact as a whole. A zoom lens for use as an image pickup optical system in such image pickup apparatuses is desired to be compact, have a high zoom ratio, offer a wide angle of view, and deliver high optical performance over the entire zoom range. The zoom lens is also desired to be short in the optical axis direction.
The following positive lead type zoom lens is known as a zoom lens that provides both compactness and a high zoom ratio. This zoom lens includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a rear lens group including one or more lens units.
Japanese Patent Application Laid-Open No. 2014-21367 discloses a positive lead type zoom lens with a rear lens group including a fourth lens unit having a negative refractive power and a fifth lens unit having a positive refractive power. Japanese Patent Application Laid-Open No. 2013-235060 discloses a zoom lens with a rear lens group including a fourth lens unit having a positive refractive power and a fifth lens unit having a positive refractive power. Japanese Patent Application Laid-Open No. 2013-80153 discloses a zoom lens with a rear lens group including a fourth lens unit having a negative refractive power, a fifth lens unit having a positive refractive power, and a sixth lens unit having a positive refractive power.
Aiming for a high zoom ratio in a positive lead type zoom lens tends to cause various aberrations, such as spherical aberration, coma, and chromatic aberration, in a telephoto zoom range.
In addition, excessive reduction in the positive refractive power of the first lens unit increases the amount by which the first lens unit moves when zooming, and consequently increases the overall size of the zoom lens.
Thus, an appropriate setting of the refractive power of the first lens unit is important in a positive lead type zoom lens in order to achieve both compactness and a high zoom ratio while favorably correcting the various aberrations. It is also important to appropriately set the amounts by which the second lens unit and the third lens unit move when zooming.
When these lens units are not appropriately configured, it is difficult to obtain a zoom lens which is compact and has a high zoom ratio while favorably correcting the various aberrations.